1. Target Injection Update
Cryogenic sabot coil resistance testing
Injector cost savings from new chamber design
Reduced velocity target injection
Remy Gallix, Dan Goodin, Dean Morris, and Robert Kratz
Presented by Ron Petzoldt
Naval Research Laboratory HAPL Meeting
March 3-4, 2005

2. Non-contacting Electromagnetic Injector (~400 m/s)
An attractive force, self-centering, non-contacting accelerator has been proposed for IFE target injection (A. Robson)
With an attractively accelerated sabot, sabot current would be imposed in a pre-injector
A critical issue for this concept is the residence time of the sabot current (requires low resistivity) Fr Fz
High purity aluminum has low density and low resistivity at cryogenic temperatures Fr
Sabot Coil
Accelerating Coil

3. Attractive Force EM Injector Requires a Long Inductance/Resistance (L/R) Time Sabot Coil
L/R must be much greater than acceleration time (L/R>> 25 ms)
where ao is the inner radius of a Brooks coil,
b is the packing fraction, and h is the resistivity in W-cm.
Lowest reported resistivity for ultra-pure Al h = 4x10-10 W-cm and h = 2x10-9 W-cm at 15 K in 1 Tesla field.
99.999% pure Al wire
For ao = 0.4 cm and b = 0.75 this translates to:
L/R = 800 ms (no field) and L/R = 160 ms (1 Tesla)
In practice, metal impurity, wire winding (cold working), and joint resistance can decrease L/R
8 mm
What L/R can we obtain in a prototypical sabot coil?

4. We Performed a Coil Current Decay Time Measurement in High Magnetic Field Down to 4 K
The experiment includes three separate coils
Induction field coil
Pickup coil
Induction field circuit
G10 form containing all 3 coils
Sabot coil
We induce a current in the closed sabot coil by rapidly stopping the induction coil field
We measure pickup coil voltage to determine the sabot coil current decay time constant
Induction current
Sabot current
Pickup coil voltage
…This would be easy except for the addition of cryogenics and high magnetic field

5. Cryogenic Measurements Were Made In up to 0.9 Tesla Magnetic Fields
Pressure relief
Vent
He Liquid
Magnet
Coils
Magnet
G10 box
He gas
Cryostat
…Tests were run from 4 K up to room temperature

6. Tests were conducted in collaboration with GA’s EM Systems
Magnet tooling
Test area
Some current EM systems projects
Urban Maglev
Superconducting
Homopolar motor
EM aircraft
Launcher
…Leveraging experience in other GA divisions

7. Magnetic Field Decreases L/R at Cryogenic Temperatures
15 K pickup coil V vs t with 0.9 Tesla field
Natural log of 15 K data (B=0.9T)
At 15 K (Soldered)
L/R = 53 ms (B=0 T)
L/R = 32 ms (B=0.9 T)
= 1s / 31.5
…but we wanted >>25 ms

8. Annealing and Welding Coil Substantially Improved L/R
15 K
At 15 K (Welded and Annealed), L/R = 170 ms (B=0 T), L/R = 72 ms (B=0.9 T)
Further improvements may be possible
- Next step sabot-to-sabot consistency and refinement of techniques
Larger coil size would increase time constant but increases mass and cost
…This indicates that L/R will be sufficient

9. The Magnetic Confinement Concept Substantially Changes the Target Injection Requirements
Target survival (> ~25 m/s injection velocity)
Only one target in chamber at a time
(> ~32 m/s at 5 Hz)
At this point, we are evaluating ~50 m/s
13 cm acceleration at 10,000 m/s2
Opens door for other injection mechanisms
(Mechanical, pneumatic, electric, etc.)
Without gas in chamber, ±1 mm placement accuracy has been discussed - a challenge to be demonstrated
Without sabot separation and with in-chamber tracking, the target flight distance could be reduced from 17 m to ~10 m
…Magnetic confinement should make target injection easier (i.e. slower)

10. Calculations also indicate that plasma heating is dramatically reduced with a lower gas density *
Non-radiative target heating vs time
Plasma density and temperature vs time for DT gas
Non-radiative target heating
In-chamber interval
In-chamber interval
1-D results for 10 m radius chamber
1013/cm3 = 0.3 mT at 300 K
Prediction = non-radiative heat load < 0.1 W/cm2 at 100 ms after ignition = acceptable heat load
*Ref: Simulation of afterglow plasma evolution in an inertial fusion energy chamber
B.K. Frolov, A.Yu. Pigarov, S.I. Krasheninnikov, R.W. Petzoldt, D.T. Goodin
Journal of Nuclear Materials 337–339 (2005) 206–210
…Simplified injection concepts are being evaluated

11. Low-speed Mechanical Injector Concepts
OBJECTIVE: Inject bare DD targets into vacuum
at 5 Hz (160 million cycles /year),
with v = 50 m/s upwards
and acceleration a ≤ 10,000 m/s2,
without introducing gas into chamber.
A SOLUTION: Use reciprocating pusher to inject a target every 0.2 s.
OPTIMUM: For minimum stroke use maximum constant acceleration: e.g., 10,000 m/s2 for 5 ms gives v = 50 m/s in 125 mm.

12. Conceptually- Targets could be Transferred from Cryogenic Fluidized Bed to Mechanical Injector
Targets accelerated out of tray
Target injector
Many linear actuator options
Mechanical
Pneumatic
Coil gun
Rotary tray

13. Injector Actuator Options…
Simple spring - doesn’t work
Geared Crank or Cam
Insufficient energy
per mass
Sinusoidal motion
Long stroke bellows
Extra revolutions between strokes
Coil gun
No dynamic vacuum seal
Cooling and electrical feed-throughs into vacuum
Pneumatic
Drive cylinder inside or outside vacuum
Coil or iron insert
Traditional accelerator options are also easier at low speed
- Electrostatic, induction accelerator, rail gun, ….

14. Target injection cost comparison for an nth of a kind plant
A 50 m/s Mechanical Injector Should Significantly Reduce IFE Target Injection Costs
Mechanical
Injection
EM Injection
Velocity
Type
Staffing at $60/hr
(5 Hz)
Cap. Cost
Total per target (5 Hz)
Total per year
50 m/s
Mechanical
2 Persons
($ per target)
$400 k
($ )
($0.0069)
$1.09 M
400 m/s
EM (includes pre-injector)
3 Persons
($0.010 per target)
$ 6 M
($0.0036)
($0.0136)
$2.14 M
Target injection cost comparison for an nth of a kind plant
*Assumes 10,000 m/s2 acceleration

15. Summary and Conclusions…
Measurement of EM injector sabot coil current decay down to 4 K and up to 0.9 Tesla show sufficient residence time is achievable
Magnetic protected chamber substantially changes target injection requirements
Velocities like 50 m/s allow much shorter acceleration length
Alternate injection concepts are being considered
“nth-of-a-kind” injection costs should be reduced for power plants
Simplicity and reliability should be enhanced
0.0001
0.001
0.01
0.1 1 10
100
1000
Temperature (K)
Time Constant (s)